1. Field of the Invention
The present invention relates to a fence valve for catching undesirable materials in a drain or sewer pipe. More specifically, the invention is directed to a fence valve having an indicator with adjustable sensitivity for alerting the user when such undesirable materials have been caught by the fence valve.
2. Description of Related Art
Fence valves are utilized in drain and sewer pipes to capture undesirable materials that tend to clog the pipes. Example prior fence valves have been described in U.S. Pat. Nos. 4,932,080, 4,996,725, 5,027,447, and 6,880,178.
A fence valve having an indicator for alerting the user when undesirable materials have been captured is described in U.S. Pat. No. 6,880,178. The described fence valve has an indicator that is located at the top of a tubular member that extends through the housing of the fence valve. At the bottom of the tubular member is a hook that extends out of the housing of the fence valve and into a drain or sewer pipe to catch the undesirable materials. Disposed within the fence valve between the indicator and a spacer and surrounding the tubular member is a kinetic energy store in the form of a spring. The housing in the area of the indicator and the spring is transparent. When the hook catches undesirable material, the weight of the material places a downward force on the tubular member which causes the indicator to move in a downward direction within the transparent housing and compress the spring. By looking through the housing and visually observing the position of the indicator and the compression of the spring, a user can determine when undesirable material has been captured by the hook of the fence valve.
A significant drawback to prior fence valves, including the valve described in U.S. Pat. No. 6,880,178 is that the sensitivity of the fence valve cannot be adjusted and is dependent on the mechanical resistance provided by the spring.